1. Field of Invention
This invention relates generally to microfluidic systems, and, in particular, to a microfluidic device in which the operation is conducted entirely without the benefit of an external fluidic driver.
2. Description of the Prior Art
Microfluidic devices have become very popular in recent years for performing analytical testing. Using tools developed by the semiconductor industry to miniaturize electronics, it has become possible to fabricate intricate fluid systems which can be inexpensively mass produced. Systems have been developed to perform a variety of analytical techniques for the acquisition and processing of information.
U.S. Pat. No. 5,716,852 is an example of such a device. This patent teaches a microfluidic system for detecting the presence of analyte particles in a sample stream using a laminar flow channel having at least two input channels which provide an indicator stream and a sample stream, where the laminar flow channel has a depth sufficiently small to allow laminar flow of the streams and length sufficient to allow diffusion of particles of the analyte into the indicator stream to form a detection area, and having an outlet out of the channel to form a single mixed stream. This device, which is known as a T-sensor, allows the movement of different fluidic layers next to each other within a channel without mixing other than by diffusion.
Microfluidic systems of this type require some type of external fluidic driver, such as piezoelectric pumps, microsyringe pumps, electroosmotic pumps and the like, to operate. It would be desirable, in many situations, to produce a device which is entirely driven by a readily available force, such as gravity, capillary action, absorption in porous materials, chemically induced pressures or vacuums (e.g., by a reaction of water with a drying agent), or by vacuum and pressure generated by simple manual action, rather than by an external fluidic driver requiring a separate power source having moving parts. Such a device could be extremely simple to operate, could be manufactured very inexpensively, and could be used to perform many diagnostic assays using a variety of microfluidic methods.
Accordingly, it is an object of the present invention to provide a microfluidic device which can be operating without a fluid driver that requires a power source.
It is a further object of the present invention to provide a low cost disposable qualitative assay which can be adapted to medical or environmental uses, among others.
It is still a further object of the present invention to provide a simple microfluidic system which can perform analytical functions without the necessity of an external electrical or mechanical fluid driver system.
These and other objects are accomplished in the present invention by a simple cartridge device containing microfluidic channels which perform a variety of analytical techniques for the acquisition of information without the use of any electrical or mechanical driving forces applied to the cartridge. The cartridge may be constructed from a single material, such as plastic, by conventional manufacturing methods, such as injection molding, to create a low cost device which can be discarded after a single use. Inherently available forces such as gravity, hydrostatic pressure, capillary force, absorptive force manually generated pressure, or vacuum, move the fluids through the microfluidic channels to accomplish the desired analytical analyses. Other applications for this technology include toys and advertising devices.